Semiconductor devices, like most electronic products, are sensitive in their operation to supplied voltage levels. If voltage levels at working parts are lower than specified minimum requirements, the parts may malfunction. If voltage levels are higher than specified maximum requirements, the parts may malfunction and can also suffer catastrophic failure. In semiconductor memory devices, for example, such as Dynamic Random Access Memories (DRAMs), inadequate voltage levels may cause memory parts to malfunction by reading out or storing incorrect information. Such low voltage failures are often difficult to detect, and even when they are detected the resultant functional and data errors can seldom be recovered.
Often, the semiconductor device is still operational when the voltage levels become marginal causing the device to potentially fail in some aspect. For example, a memory device may not meet its full timing specifications at low voltages, resulting in a failure to read correct data. Even though the read data may be correct, the access time until correct data is available may be longer than designated by the device specification. Similarly, a low voltage level may result in the memory device's bit-cell capacitors not having enough time to fully charge during a write cycle, even though they would work correctly if given additional time to complete the write cycle. In such a case, the bit-cells cannot be properly read and the data becomes corrupted.
There are many causes for unsuitable voltage levels to semiconductor devices, such as power supply errors and power distribution path effects. Power supply errors may result when the power supply is inadequate, misadjusted, or fails altogether. Power distribution path effects influence voltage levels, for example, through transient noise signals, inductance, and/or resistance in power distribution paths. As semiconductor device activity increases, these power distribution path effects often add together and further increase the chances of data and functional errors.
Historically, voltage sensors have been used to detect the voltage levels coming directly from the power supplies. However, these devices are limited to sensing voltage errors in the supply voltage. These systems are not capable of detecting whether voltage levels are unsuitable at specific locations (e.g., circuits) within the semiconductor device itself. Thus, these devices do not detect unsuitable voltage levels not caused by the voltage source itself, such as the distribution path effects described above.
In view of the shortcomings in the prior art, it would be advantageous to provide a semiconductor device capable of sensing and/or reporting voltage levels at operational circuits within the semiconductor device.